CVE-2017-7344 in FortiClient
Summary
by MITRE
A privilege escalation in Fortinet FortiClient Windows 5.4.3 and earlier as well as 5.6.0 allows attacker to gain privilege via exploiting the Windows "security alert" dialog thereby popping up when the "VPN before logon" feature is enabled and an untrusted certificate chain.
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Analysis
by VulDB Data Team • 01/27/2021
The vulnerability identified as CVE-2017-7344 represents a critical privilege escalation flaw affecting Fortinet FortiClient Windows versions 5.4.3 and earlier, as well as version 5.6.0. This security weakness specifically targets the Windows security alert dialog mechanism that appears when the VPN before logon feature is activated, creating an exploitable condition that allows attackers to elevate their privileges from standard user level to administrative rights. The vulnerability stems from improper handling of certificate validation within the FortiClient application when establishing VPN connections during the pre-login phase of Windows authentication.
The technical implementation of this flaw occurs through the manipulation of the Windows security alert dialog that appears when an untrusted certificate chain is encountered during the VPN connection process. When the VPN before logon feature is enabled, FortiClient presents a security dialog to users that displays certificate information and prompts for trust decisions. Attackers can exploit this mechanism by crafting malicious certificate chains that trigger the security dialog in a way that allows them to execute arbitrary code with elevated privileges. This occurs because the application fails to properly validate the certificate chain before presenting the security dialog, creating a window where malicious actors can intercept and manipulate the authentication process.
The operational impact of CVE-2017-7344 extends beyond simple privilege escalation as it provides attackers with a persistent foothold within the target environment. Once elevated to administrator level, threat actors can establish backdoors, modify system configurations, access sensitive data, and move laterally throughout the network without detection. The vulnerability is particularly dangerous because it operates during the pre-login phase when users are not yet authenticated, making it difficult to detect through traditional monitoring mechanisms. This characteristic aligns with ATT&CK technique T1068 which describes the exploitation of local system privileges to gain higher-level access, and CWE-284 which addresses improper privilege management in software applications.
Organizations affected by this vulnerability should implement immediate mitigations including updating to FortiClient versions 5.4.4 or later where the issue has been resolved, disabling the VPN before logon feature until patches are applied, and implementing additional security controls such as certificate pinning and enhanced monitoring of Windows security alert dialog interactions. The vulnerability demonstrates the importance of proper certificate validation procedures and the risks associated with applications that interact with Windows security dialogs during authentication processes, particularly those that operate in pre-login contexts. Security teams should also consider implementing network segmentation and access controls to limit the potential damage from successful exploitation of this privilege escalation vulnerability.